A multireference second-order perturbation theory using a restricted active space self-consistent field wave function as reference (RASPT2/RASSCF) is described. This model is particularly effective for cases where a chemical system requires a balanced orbital active space that is too large to be addressed by the complete active space self-consistent field model with or without second-order perturbation theory (CASPT2 or CASSCF, respectively). Rather than permitting all possible electronic configurations of the electrons in the active space to appear in the reference wave function, certain orbitals are sequestered into two subspaces that permit a maximum number of occupations or holes, respectively, in any given configuration, thereby reducing the total number of possible configurations. Subsequent second-order perturbation theory captures additional dynamical correlation effects. Applications of the theory to the electronic structure of complexes involved in the activation of molecular oxygen by mono- and binuclear copper complexes are presented. In the mononuclear case, RASPT2 and CASPT2 provide very similar results. In the binuclear cases, however, only RASPT2 proves quantitatively useful, owing to the very large size of the necessary active space.
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28 May 2008
Research Article|
May 30 2008
The restricted active space followed by second-order perturbation theory method: Theory and application to the study of and systems
Per Åke Malmqvist;
Per Åke Malmqvist
1Department of Theoretical Chemistry,
University of Lund
, P.O. Box 124, S-221 00 Lund, Sweden
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Kristine Pierloot;
Kristine Pierloot
2Department of Chemistry,
University of Leuven
, Celestijnenlaan 200 F, bus 2404, B-3001 Leuven, Belgium
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Abdul Rehaman Moughal Shahi;
Abdul Rehaman Moughal Shahi
3Department of Physical Chemistry,
University of Geneva
, 30 Quai Ernest Ansermet, CH-1211 Geneva, Switzerland
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Christopher J. Cramer;
Christopher J. Cramer
4Department of Chemistry and Supercomputing Institute,
University of Minnesota
, 207 Pleasant St. SE, Minneapolis, Minnesota 55455-0431, USA
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Laura Gagliardi
Laura Gagliardi
a)
3Department of Physical Chemistry,
University of Geneva
, 30 Quai Ernest Ansermet, CH-1211 Geneva, Switzerland
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a)
Electronic mail: laura.gagliardi@unige.ch.
J. Chem. Phys. 128, 204109 (2008)
Article history
Received:
February 25 2008
Accepted:
April 14 2008
Citation
Per Åke Malmqvist, Kristine Pierloot, Abdul Rehaman Moughal Shahi, Christopher J. Cramer, Laura Gagliardi; The restricted active space followed by second-order perturbation theory method: Theory and application to the study of and systems. J. Chem. Phys. 28 May 2008; 128 (20): 204109. https://doi.org/10.1063/1.2920188
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